Amplification system



May 20, 1930.

s. COHEN AMPLIFI CAT ION SYSTEM Filed Feb. 21 1925 mam we:

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Patented May 20, 1930 uNrrEn s'rArs PATENT OFFl'CE SAMUEL COHEN, F BROOKLYN, NEW YORK AMPLIFICATION' SYSTEM Application filed February 21,1925. Serial- No. 10,885.

My invention relates broadly to electron tube amplification systems, and more particularly to means for preventing theinteraction of the electrical circuits of an amplification system with an increase in the oper ating efiiciency thereof for the amplification of feeble electrical currents to a considerable degree.

One of the objects of my invention is to provide a multi-stage electron tube amplivide an impedance system interposedbetween the input and output circuits of the electron tubes in a cascade amplification system with means for varying the value of the impedance through minute degrees for selecting a value of impedance precisely adapted for the characteristics of the tubes in the amplification system.

Still another object of my invention'is to provide an impedance circuit for supplementing the coupling of a plurality of elec tron tubes forming an amplification system, which impedance circuit comprises in part an electron stream arranged to be controlled by variation of the incandescence of a cathode in such manner that fine adjustments in the value of impedance may be obtained for selecting that value which cooperates with the particular characteristics ofthe 0 tubes employed in the amplification system for dissipating oscillatory currents in the circuits.

A still further object of my invention is to provide a construction of impedance circuit supplementing the couplings in an electron tube amplification system whereby electronic bombardment from a plurality of independent cathodes upon a common cathode maybe arranged to form impedance paths as far dissipating undesired oscillatory currents in the electron tube circuits of the amplification system.

My invention has particular application to radio frequency amplification systems where the incoming signaling currents are amplified at a frequency substantially above that of audition. At radio frequencies the capacity effects inherent in the electron tubes of an amplification system introduce a serious problem, and the circuits inter-connecting the electrodes of the tubes often interact upon each other resulting in self-excitation of the amplification system rather than amplification of the desired signaling energy. By my present invention I provide a'construction of impedance circuit by which the oscillatory currents existent in the input and output circuits of the several tubes of the amplification system may be dissipated to such an extent that the amplification system may be stabilized and operate efiiciently for the transferring of signaling currents without interference from undesired oscillatory currents. V 7

'My invention will bemore fully understood from the following specification hereinafter following and the accompanying drawings, in which: 7

Figure 1 is a theoretical diagram representing the arrangement of the elements within an electron tube and indicating the inherent capacities existent between the electrodes of the tube; Fig. 2 is a theoretical wiring diagram illustrated in lieu of the inherent capacities existent between the electrodes of an electron tube; Fig. 3 is a diagrammatic view of one stage of electron tube amplification showing the application of the impedance circuit constructed in accordancewith my invention; and Fig. 4 shows the application of my invention to a multi-stage radio frequency amplifier connected before a detector in a radio receiving apparatus.

My invention contemplates the construction of an impedance circuit which includes in part a path formed by an electronic stream,- which stream may be varied by controlling the degree pf incandescence of a heated cathode with n an exhausted receptacle. The impeaasea circuit is between a point in the input circuit of the electron tube and a point in the output circuit of the electron tube including the inductance of the output circuit. The impedance circuit thereby consists of a composite resistance, inductance, and capacity resulting from the inherent intra-electrode capacity of the impedance device and is electrically operative to dissipate oscillatory currents in the input and output circuits of each of the electron tubes in the amplification system. Inasmuch as the amplification system is relieved of interference arising from undesired oscillatory currents, a relatively large number of stages of amplification may be employed. Where a plurality of stages are employed I may provide an exhausted receptacle in which a plurality of independent cathodes may be employed to direct independent electron streams upon a common anode with independent connections between each of the cathodes with the input circuits of the several tubes, and a common connection between points in the output circuits of the several tubes and the common anode whereby undesired oscillatory currents may be dissipated.

Referring to the drawings in more detail, Fig. 1 designates an electron tube wherein the grid, filament and plate electrodes have been designated by reference letters G, F and P. The inherent electrical capacity existing between the grid and plate electrodes has been marked G P. The inherent capacity between the grid and the filament electrodes has been designated G F, while the capacity existing between the filament and the plate has been represented by F P. The electrical relationships of these capacities when employed in an amplification circuit has been shown more clearly in Fi g. 2, wherein an input circuit, including primary inductance 1, is coupled with a secondary inductance L tuned by condenser C The electron tube has been shown by the representation of its fundamental electrical capacities as designated in Fig. 1. In the output circuit of the amplification system an inductance L is provided in series with the high potential battery B. An inductance L is coupled to the inductance L forming the output circuit of the amplification system. The impedance circuit RC is connected between a point 6 in the input circuit of the amplification system and point 7 on the opposite side of the output circuit inductance L and Operates to dissipate oscillatory currents whereby the operation of the amplification system is stabilized.

The application of the principles illustrated in Fig. 2 will be more clearly understood by reference to Fig. 3, in which the electron tube has been designated by reference character 2 having filament electrode 8, grid electrode a, and plate electrode 5. The impedance circuitis represented as consisting in part of the evacuated container 8 having a cold anode 10 and a hot cathode 9. The cathode is energized from a suitable source of energy, represented. at 11, controlled through rheostat 12. The impedance circuit effectively includes the capacity existent between electrodes 9 and 10 and the inductance L related to the input and output circuits of the electron tube 2 at points 6 and 7 in the input and output circuits respectively. The impedance value can be changed at will by altering the filament emission of the heated cathode 9 by regulation of the rlicostat 12. The change in the impedance value operates to vary the degree of dissipation of oscillatory currents tor eliminating the possibility of local oscillations in the amplification system.

In Fig. 4 one of the practical applications of my invention has been shown in connection with a two-stage radio frequency amplifier comprising electron tubes 2 and 17 preceding the detector tube 21 in the radio receiving circuit. An antenna ground system 1 1 and 15 is connected to the primary or input inductance 1 coupled as hereinbefore explained in connection with Figs. 2 and 3 to the secondary inductance L included in the input circuit of the radio frequency amplification tube 2. The inductance In; in the output circuit of tube 2 is coupled with the inductance L in the input circuit of radio frequency amplification tube 17. The secondary L is tuned by variable condenser 16. Primary inductance 18 is included in the output circuit of tube 17 and is coupled with secondary inductance 19 connected to the input circuit of detector tube 21. Detector tube 21 includes grid leak 22 in the grid circuit thereof. The inductance 19 is tuned by variable condenser 20. A suitable responsive device, as indicated at 28, is connected in the output circuit of the detector 21. The tubes have their cathodes heated from a common battery designated A in the drawing and high potential is supplied to the anode circuits from battery B with a suitable tapped connection taken to the anode of the detector circuit 21. A condenser 24: is provided for by-passing high frequency currents around the high potential supply system. The impedance device comprises evacuated vessel 25 containing a plurality of electron emitting cathodes designated at 27 and 28, each heated from independent sources of energy represented at 29 and 31, the value of the energy being controlled through independent rheostats 30 and 32. The independent cathodes 27 and 28 are connected with points in the input circuits of the several tubes designated at 6 and 35. A common anode 26 is provided connected to points in the output circuits of the several tubes designated at 7. It will be observed that the point at which the anode 26 connected with the output circuits is so positioned as to include the inductances L and 18 of the output circuits in series with the anodes of the several tubes in the amplification system. The incandescence of the electron emitting cathodes can be Varied to thereby change the impedance of the circuit in accordance with the characteristics of the particular tubes in the amplification system. Shouldthe tubes in the amplification system vary in their characteristics, the degree of incandescence of any one of the cathodes may be changed to thereby vary the impedance of the circuit by reason of the change in the bombardment by the anode of the electrons emitted from the cathodes. The ionized path or electronic stream is thereby employed as a portion of the impedance circuit and enables accurate selection of the total impedance connected in circuit with the electron tubes.

I have represented a radio frequency amplification system having two electron tube stages, and have illustrated an impedance device having a pair of incandescent cathodes and a single anode. I desire it to be understood however that the system is equally applicable to amplification circuits of a great many stages and that in order to control and stabilize the same the impedance device may include a number of incandescent cathodes corresponding to the number of electron tube stages in the system. The. anode may be positioned centrally within the evacuated vessel while the several cathodes may be positioned about the central anode and be independently controlled as heretofore described. The employment of the impedances in relation to the input and output circuits of the tubes, as I have explained, operates to dissipate the oscillatory currents in the input and output circuits whereby the systenr becomes stable and undesired oscillatory currents are eliminated.

"While I have described by invention in certain particular embodiments I desire that it be understood that the applications thereof have been shown for illustrative purposes and that no limitations upon the invention are intended other than are imposed by the scope of the appended claims.

Having thus described my invention, what I claim and desire to secure by Letters Patent of the United States is as follows:

1. An amplification system comprising a plurality of electron tubes each having grid,

lament and plate electrodes, input circuits interconnecting said grid and filament electrodes, output circuits interconnecting said plate and filament electrodes, means coupling the output circuit of one of said tubes with the input circuit of a succeeding tube, and a composite impedance path having its ends connected with each of said input circuits with an intermediate portion of said path connected to each of said out ut circuits, the paths thus established consisting in part of independent electron streams whereby undesired oscillatory currents may be prevented in said amplification system.

2. An amplification system comprising in combination a plurality of electron tubes each having grid, filament and plate electrodes, input circuits interconnecting said grid and filament electrodes, output circuits interconnecting said plate and filament electrodes, means coupling the output circuit of one of said tubes with the input circuit of afsucceeding tube, and a plurality of impedance paths formed between a plurality of independent and filament electrodes, output circuits -inter-' connecting said plate and filament electrodes, means coupling the output circuit of one of said tubes with the input circuit of a succeeding tube, an impedance element comprising an evacuated vessel, a plurality of independent electron emitting cathodes, a common anode, connections between one ot'said electron emitting cathodes and a point in one of said input circuits, a connection between another of said electron emittin cathode and the input circuit of the next succeeding electron tube and a connection between said anode and said output circuits whereby oscillatory currents in the input and output circuits of each of said tubes may be dissipated preventing oscillatory currents in said amplification system.

4. An amplification system comprising in combination a plurality of electron tubes each having grid, filament and plate electrodes, input circuits connected with said grid and filament electrodes, output circuits interconnecting said plate and filament electrodes, means coupling the output circuit of one of said tubes with the input circuit of a succeeding tube, an impedance element comprising an evacuated vessel, a plurality of independent electron emitting cathodes, a common anode,

a connection between one of said electron emitting cathodes and a point in one of said input circuit-s, a connection between another of said electron emitting cathode and the input circuit of the next succeeding electron tube and a connection between said anode and points in each of said output circuits, the electron emitting cathodes having means for c0ntrolling the electron emission thereof and the bombardment of said anode whereby the intensity of the electron emission may be varied for dissipating oscillatory currents in the input and output circuits of each of said electron tubes.

5. An amplification system comprising in combination a plurality of electron tubes each having grid, filament and plate electrodes, input circuits connected with said grid and filament electrodes, output circuits interconnecting said plate and filament electrodes means coupling the output circuit of one 0 said tubes with the input circuit of a succeeding tube, an impedance element comprising an evacuated vessel, a central anode, a plurality of independent electron emitting cathodes spaced the'rearound and each having means for independently adjusting the electron emitting temperature thereof, a connection between one of said electron emitting cathodes and a point in one of said input circuits, a connection between another of said electron emitting cathodes and the input circuit of the next succeeding electron tube and a connection between said central anode and a point in said output circuits whereby undesired oscillatory currents in all of said circuits may be substantially eliminated.

In testimony whereof I hereby aflix my signature.

SAMUEL COHEN. 

